Estimate the calorie count of this door handle: https://m.youtube.com/watch?v=VDSzY52Mkrw&pp=0gcJCVACo7VqN5t...

Extreme example perhaps, but no, you can't just turn pixels into calories. Right now I'd be impressed if we could reliably estimate volume to within 30% from a photo, but even with that correct the contents of the food can easily be way off without visible sign.